On the relative Nash approximation of analytic maps.
On the seperation of basic semialgebraic sets by polynomials.
On the space of morphisms into generic real algebraic varieties
We introduce a notion of generic real algebraic variety and we study the space of morphisms into these varieties. Let be a real algebraic variety. We say that is generic if there exist a finite family of irreducible real algebraic curves with genus and a biregular embedding of into the product variety . A bijective map from a real algebraic variety to is called weak change of the algebraic structure of if it is regular and its inverse is a Nash map. Generic real algebraic varieties...
On the space of real algebraic morphisms
In this Note, we announce several results concerning basic properties of the spaces of morphisms between real algebraic varieties. Our results show a surprising intrinsic rigidity of Real Algebraic Geometry and illustrate the great distance which, in some sense, exists between this geometry and Real Nash one. Let us give an example of this rigidity. An affine real algebraic variety is rigid if, for each affine irreducible real algebraic variety , the set of all nonconstant regular morphisms from...
On total reality of meromorphic functions
We show that, if a meromorphic function of degree at most four on a real algebraic curve of an arbitrary genus has only real critical points, then it is conjugate to a real meromorphic function by a suitable projective automorphism of the image.
On Witt rings of function fields of real analytic surfaces and curves.
Let V be a paracompact connected real analytic manifold of dimension 1 or 2, i.e. a smooth curve or surface. We consider it as a subset of some complex analytic manifold VC of the same dimension. Moreover by a prime divisor of V we shall mean the irreducible germ along V of a codimension one subvariety of VC which is an invariant of the complex conjugation. This notion is independent of the choice of the complexification VC. In the one-dimensional case prime divisors are just points, in the two-dimensional...
Optimal degree construction of real algebraic plane nodal curves with prescribed topology. I. The orientable case.
We study a constructive method to find an algebraic curve in the real projective plane with a (possibly singular) topological type given in advance. Our method works if the topological model T to be realized has only double singularities and gives an algebraic curve of degree 2N+2K, where N and K are the numbers of double points and connected components of T. This degree is optimal in the sense that for any choice of the numbers N and K there exist models which cannot be realized algebraically with...
Orbit theorems for semigroup of regular morphisms and nonlinear discrete time systems
Overdetermined Strata in General Families of Polynomials
2000 Mathematics Subject Classification: 12D10.In the paper we give different examples of overdetermined strata.
Parusinski's “Key Lemma” via algebraic geometry.
Polynomial inequalities on algebraic sets
We give an estimate of Siciak’s extremal function for compact subsets of algebraic varieties in (resp. ). As an application we obtain Bernstein-Walsh and tangential Markov type inequalities for (the traces of) polynomials on algebraic sets.
Polynomial mappings form products of algebraic sets into spheres.
Positive polynomials and hyperdeterminants
Let F be a homogeneous real polynomial of even degree in any number of variables. We consider the problem of giving explicit conditions on the coefficients so that F is positive definite or positive semi-definite. In this note we produce a necessary condition for positivity, and a sufficient condition for non-negativity, in terms of positivity or semi-positivity of a one-variable characteristic polynomial of F. Also, we revisit the known sufficient condition in terms of Hankel matrices.
Préhistoire de la géométrie algébrique réelle : de Descartes à Tarski
Projective modules over real affine algebras.
Prolongements en fonctions algébriquement constructibles.
In this paper we consider the following question: Let S be a semialgebraic subset of a real algebraic set V, and let φ: S → Z be a function on S. Is φ the restriction of an algebraically constructible function on V, i.e. a sum of signs of polynomials on V? We give an effective method to answer this question when φ(S) ⊂ {-1,1} or dim S ≤ 2 or S is basic.
Pseudo-real principal Higgs bundles on compact Kähler manifolds
Let be a compact connected Kähler manifold equipped with an anti-holomorphic involution which is compatible with the Kähler structure. Let be a connected complex reductive affine algebraic group equipped with a real form . We define pseudo-real principal -bundles on . These are generalizations of real algebraic principal -bundles over a real algebraic variety. Next we define stable, semistable and polystable pseudo-real principal -bundles. Their relationships with the usual stable, semistable...
Quadratic mappings and configuration spaces
We discuss some approaches to the topological study of real quadratic mappings. Two effective methods of computing the Euler characteristics of fibers are presented which enable one to obtain comprehensive results for quadratic mappings with two-dimensional fibers. As an illustration we obtain a complete topological classification of configuration spaces of planar pentagons.
Quadratische Formen über affinen Algebren und ein algebraischer Beweis des Satzes von Borsuk-Ulam.
Quadrics through a set of points and their syzygies.